SPF (Sender Policy Framework or Sender Permitted From), Domainkeys, and DKIM (DomainKeys Identified Mail) are methods to authenticate mail senders and detect incoming mail that was not sent by whom it says it was sent. This can help to fight spam. For example, if spammers can no longer hide their domain identity by faking their sending domains, they could effectively be blacklisted.

SPF does this by adding a TXT record to the DNS (Domain Name System) stating which servers are allowed to send mail from a particular domain.

Domainkeys and its followup, DKIM add an electronic signature to each mail, whose public key is advertised also as TXT record in the DNS, usually under default._domainkey.domain.com, where domain.com is replaced with the actual domain. The signature can be added by the local email client or by the sending mail server.

If you have a functioning Domainkeys or DKIM installation, you can test it with the following tools. "Send an email" means to send just any email, which can be empty.

• Send an email to: dk©dk.crynwr.com. The receiving server will forward your mail to the following indented addresses, so if this one works sufficiently well and you receive at least one auto-response, you don't need to send any more mails.
  • Send an email to: autorespond+dk©dk.elandsys.com
  • Send an email to: sa-test©sendmail.net
• Check this list for more good checking methods and addresses: http://www.smartertools.com/forums/p/20373/56544.aspx

  The best of that bunch seems to be to send an email to: check-auth©verifier.port25.com

In the automatic replies look for status: good, test: pass, or a similar message.

If you know any further test systems or if you find that one of the above ones consistently fails, please send an email to the webmaster.